Method and system using refractive beam mapper having square element profiles to reduce moire interference in a display system including multiple displays

ABSTRACT

A multi-display system (e.g., a display including multiple display panels) includes at least first and second displays (e.g., display panels or display layers) arranged substantially parallel to each other in order to display three-dimensional (3D) features to a viewer(s). An optical element(s) such as at least a refractive beam mapper (RBM) is utilized in order to reduce moiré interference.

This application is a continuation-in-part (CIP) of U.S. patentapplication Ser. No. 15/283,621, filed Oct. 3, 2016, and thisapplication is related to and claims priority on each of provisionalU.S. Patent Application Nos. 62/281,037, filed Jan. 20, 2016 (Our Ref.6468-16); 62/280,993, filed Jan. 20, 2016 (Our Ref. 6468-17); and62/236,776, filed Oct. 2, 2015 (Our Ref. 6468-8), all of which arehereby incorporated herein by reference in their entireties.

FIELD OF THE INVENTION

This invention relates to a multi-display system (e.g., a displayincluding multiple display panels/display layers), where at least firstand second displays (e.g., display panels or display layers) arearranged substantially parallel to each other in order to displaythree-dimensional (3D) features to a viewer(s). Thus, this inventionrelates generally to displays and, more particularly, to display systemsand methods for displaying three-dimensional features.

BACKGROUND AND SUMMARY OF THE INVENTION

Traditionally, displays present information in two dimensions. Imagesdisplayed by such displays are planar images that lack depthinformation. Because people observe the world in three-dimensions, therehave been efforts to provide displays that can display objects inthree-dimensions. For example, stereo displays convey depth informationby displaying offset images that are displayed separately to the leftand right eye. When an observer views these planar images they arecombined in the brain to give a perception of depth. However, suchsystems are complex and require increased resolution and processorcomputation power to provide a realistic perception of the displayedobjects.

Multi-component displays including multiple display screens in a stackedarrangement have been developed to display real depth. Each displayscreen may display its own image to provide visual depth due to thephysical displacement of the display screens. For example, multi-displaysystems are disclosed in U.S. Patent Publication Nos. 2015/0323805 and2016/0012630, the disclosures of which are both hereby incorporatedherein by reference.

When first and second displays or display layers are conventionallystacked on each other in a multi-display system, moire interferenceoccurs. The moire interference is caused by interactions between thecolor filters within the layers when projected onto a viewer's retina.For example, when green color filters overlap, light is transmittedmaking for a comparative bright patch. When a green filter is over say ared filter, not as much light will be transmitted making for a darkregion. Since the rear and front displays or display layers haveslightly different sizes when projected onto the retina, the pixels willslowly change from being in phase to out of phase. This has the effectof producing dark and bright bands otherwise known as moireinterference.

Certain example embodiments of the instant invention provide solution(s)that make moire interference in MLD systems vanish or substantiallyvanish, but without significantly sacrificing the rear displayresolution and contrast. In certain example embodiments of thisinvention, the MLD system includes first and second displays. Arefractive beam mapper (RBM) may be utilized in order to reduce oreliminate moire interference. It has been found that square profilediffuser elements improve image quality in such MLD systems.

In example embodiments of this invention, there is provided a displaydevice comprising: a first display in a first plane for displaying afirst image; a second display in a second plane for displaying a secondimage, wherein said first and second planes are approximately parallelto each other; a beam mapping element located between the first andsecond displays and comprising a plurality of microlenses configured todirect rays output from the second display through sub-pixels of thefirst display and toward a viewer, wherein the microlenses each have asubstantially square profile as viewed from above in order to improveimage quality.

In example embodiments of this invention, there is provided a displaydevice comprising: a first display in a first plane for displaying afirst image; a second display in a second plane for displaying a secondimage, wherein said first and second planes are approximately parallelto each other; and a beam mapping element (e.g., refractive beam mapper)located between the first and second displays and comprising a pluralityof microlenses configured to direct incident rays from the seconddisplay in a pseudo random manner through sub-pixels of the firstdisplay and toward a viewer.

In certain example embodiments of this invention, there is provideddisplay device comprising: a first display in a first plane fordisplaying a first image; a second display in a second plane fordisplaying a second image, wherein said first and second planes areapproximately parallel to each other; a refractive beam mapper locatedbetween the first and second displays and comprising an array of beammapping elements configured to direct rays output from the seconddisplay through sub-pixels of the first display and toward a viewer,wherein the beam mapping elements each have a substantially squareprofile.

A refractive beam mapper may or may not be used in combination withother techniques for reducing moire interference (e.g., color filteroffset or dissimilar color filter patterns on the respective displays,diffuser techniques, and/or subpixel compression) in various embodimentsof this invention.

BRIEF DESCRIPTION OF THE DRAWINGS

This patent or application file contains at least one drawing executedin color. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

These and other features and advantages may be better and morecompletely understood by reference to the following detailed descriptionof exemplary illustrative embodiments in conjunction with the drawings,of which:

FIG. 1 is a top plan view of color filters of a liquid crystal display(LCD) where pixels are the same color in each column (or row);

FIG. 2 is a top plan view of color filters of another liquid crystaldisplay (LCD) where pixels are the same color in each column (or row);

FIG. 3 is a top plan view of a MLD system resulting from the combinationof LCDs of FIGS. 1 and 2 where the LCD of FIGS. 1 and 2 are overlappedwith each other in a stacked relationship, which results in moireinterference;

FIG. 4 is a schematic diagram illustrating pseudo random mapping ofpixels of a rear display to pixels in a front display of a MLD system;

FIG. 5 is a schematic diagram illustrating a mapping element that may beused in connection with the pseudo random mapping of FIG. 4 in order toreduce moire interference (this may or may not be used in combinationwith sub-pixel compression embodiments in various embodiments of thisinvention);

FIG. 6 is a schematic side cross sectional view of a MLD according to anexample embodiment of this invention, which may be used with theembodiments of any of the figures herein;

FIG. 7 illustrates a bandwidth limited implementation of a RBM havingrefractive optics;

FIG. 8 is an intensity profile exhibiting improved super-Lorentziancharacteristics over a range of angles with p=40 and lens feature sizesless than or equal to 160 microns;

FIG. 9 is a graph illustrating that bigger microlenses will typicallyhave better anti-moiré diffuser profiles;

FIG. 10 is a schematic diagram illustrating an example fabricationprocesses for a RBM that may be used in various embodiments of thisinvention;

FIG. 11 illustrates a microlens according to an example embodiment ofthis invention;

FIG. 12 is an angle of incidence vs. transmission coefficient graph thatshows curves illustrating the transmission coefficient for S and P wavesvs. angle of incidence;

FIG. 13 is a graph showing system contrast (contrast (θi, n1, n2, N),wherein θi is the angle of incidence, n1 is the refractive index of thematerial between LCDs, n2 is the refractive index of glass, and N is thenumber of interfaces;

FIGS. 14-16 are side cross sectional views of a MLD system according toembodiments of this invention where a moire reducing element (e.g., RBM)is placed in various locations of a stack in a MLD system according tovarious embodiments of this invention (this may or may not be used incombination with sub-pixel compression in various embodiments of thisinvention).

FIG. 17 is a plan view of a diffuser including square profilemicrolenses that may be used as a moire reducing element (e.g., RBM) inany embodiment herein such as in any of FIGS. 4-7, 14-16.

FIG. 18 is a plan view representative of a perfect circular filterkernel.

FIG. 19 varies the radius of a circular kernel with respect to imagequality.

FIG. 20 is a graph comparing square and circular kernel comparisons (formicrolens profiles) with respect to image quality.

DETAILED DESCRIPTION

This invention relates to a multi-display system (e.g., a displayincluding multiple display panels), where at least first and seconddisplays (e.g., display panels or display layers) are arrangedsubstantially parallel to each other in order to displaythree-dimensional (3D) features to a viewer(s). The displays may be flator curved in different embodiments. Thus, embodiments of this inventionrelate generally to displays and, more particularly, to display systemsand methods for displaying three-dimensional features. MLDs according toexample embodiments of this invention may be used, for example, asdisplays in vehicle dashes in order to provide 3D images (e.g., forspeedometers, vehicle gauges, vehicle navigation displays, etc.).

The color moire interference problem is caused by the pattern regularityof both liquid crystal display (LCD) color filter arrays as, forexample, RGB pixels are aligned into RGB columns in both displays of aMLD system. Color moire interference may be largely prevalent in thehorizontal direction.

FIGS. 1-3 illustrate an arrangement in a MLD system which experiencesmoire interference. FIG. 1 is a top plan view of color filters/pixels ofa first liquid crystal display (LCD) where pixels or subpixels are thesame color in each column. In particular, FIG. 1 shows a LCD having aconventional red-green-blue (R-G-B) repeating pattern or arrangement,wherein the pixels or subpixels are the same color in each column.Starting from the left side of FIG. 1, the color filter stripes arearranged in vertical lines in a BGR order, and this BGR order repeatsitself over and over moving from left to right across the display ofFIG. 1. Thus, the pattern in the display or display layer of FIG. 1includes blue columns, green columns, and red columns. The green (G)columns are located between blue (B) and red (R) colored columns. Asubpixel may be considered the area of a given pixel electrode in anarea of a particular color filter. For instance, R, G and B subpixelsmay make up a pixel. Alternatively, a subpixel may be considered to be apixel. FIG. 1 is shown without color mask rotation. Conventionally, bothpanels of a multiple layered display (MLD) may be configured similarlywith such a R-G-B arrangement. The repeatable pattern may be R-G-B, orR-B-G, or any other combination.

Likewise, FIG. 2 is a top plan view of color filters/pixels/subpixels ofa second LCD where pixels or subpixels are also the same color in eachcolumn. Starting from the left side of FIG. 2, the color filter stripesare arranged in vertical lines in a RGB order, and this order repeatsitself over and over moving from left to right across FIG. 2. Therepeatable pattern may be R-G-B, or R-B-G, or any other combinationinvolving these colors. As shown in FIG. 2, like in FIG. 1, green (G)columns are located between blue (B) and red (R) colored columns.

FIG. 3 is a top plan view of a MLD system resulting from the combinationof the LCDs of FIGS. 1 and 2, one on top of the other in a stackedoverlapping relationship in a MLD system. FIG. 3 shows the mixing of thecolor filter and pixel/subpixel patterns shown in FIGS. 1 and 2. Inparticular, FIG. 3 illustrates the emergence of moire interference givenan instance where both LCDs have a similar R-G-B column arrangement,where the pixels are the same color in each column. For example, whenthe FIG. 2 pattern overlaps the FIG. 1 pattern in a MLD system, greencolor filter lines overlap (e.g., see the left portion of FIG. 3), andlight in this green filter line overlap area is transmitted through theMLD system making for a comparatively bright green patch. When a greenfilter overlaps a red filter for instance (or a blue filter is over ared filter), not as much light will be transmitted making for a darkregion (e.g., see the dark regions surrounding the green stripe at theleft side of FIG. 3). Since the rear and front displays or displaylayers have slightly different sizes when projected onto a retina, thepixels will slowly change from being in phase to out of phase. This hasthe effect of producing dark and bright bands otherwise known as moireinterference.

Embodiments of this invention address, and reduce or solve, this moireinterference problem. Certain example embodiments of the instantinvention provide solution(s) that make moire interference in MLDsystems vanish or substantially vanish, but without significantlysacrificing the rear display resolution and contrast.

In certain embodiments of this invention, a beam mapping element such asdiffractive optical element (DOE) or a refractive beam mapper (RBM)composed of many micro-lenses may be used to reduce moire interference.When an RBM is used, pseudo random mapping may be provided in order tonot introduce extra moire effects. The divergence of individual beamsmay be limited so that any point on the rear LCD is not diverted morethan one pixel distance from a straight line by the time it reaches thefront LCD in certain example embodiments. One may also laminate such abeam mapping element to the front display and optically match the mediabetween the two LCDs with a non-birefringent material in certain exampleembodiments, and such embodiments may or may not be used in combinationwith subpixel compression techniques discussed herein.

Displays or display layers herein (e.g., see front display 1 and reardisplay 2 in FIG. 6, or the corresponding displays in FIGS. 4, 5, 7,14-16) may be LCDs, OLEDs, or the like. Twisted nematic (TN) LCDs mayfollow a fairly generic pixel layout, such as a square divided intothree portions running horizontally (or vertically) with red green andblue sub-pixels. The sub-pixels may be separated by a black mask in thehorizontal and vertical directions. There is often a square protrusionin the corner of the sub-pixel to cover the drive transistor. There areseveral different types of pixel technology that enable wide screenviewing and temporal performance required for modern desktop monitorsand televisions. Embodiments of the present invention are compatiblewith all of these LCDs, since the backplanes are designed to follow thebasic RGB stripe pixel layout. As such, the backplane layout requiredfor each pixel not need to change. For example, pixel type displays bymanufacturer include: Panasonic (IPS Pro), LG Display (H-IPS & P-IPS),Hannstar (S-IPS), AU Optronics (A-MVA), Samsung (AFFS), S-LCD (S-PVA),and Sharp Corporation (ASV and MVA). In certain embodiments, bothdisplays or display layers may be OLEDs, or one display may be an OLEDand the other an LCD. Note that in OLEDs, respective sub-pixels orpixels would be filled with red, green, and blue material as the colorfilter material (as opposed to having LCD type color filters).

FIG. 6 illustrates a MLD according to an example embodiment of thisinvention, in which the stacked overlapping layers/displays of any ofthe figures herein may be provided and utilized. For example, thedisplays shown in any of FIGS. 4-5 and 14-16 may be the front 1 and rear2 displays in FIG. 6, respectively. The first display or display layerof the MLD may be element 1 (or 2), and the second display or displaylayer of the MLD may be element 2 (or 1). Display or display layer 2 isclosest to the backlight of the MLD, and it may be desirable to have itsbackplane facing the backlight system to recycle light that may passthrough row drivers, column drivers, transistors, and storagecapacitance lines into the backlight. A two polarizer configuration maybe used, as shown in the figure, and gaps may be designed to include airor material having birefringence designed to maintain black state of thedisplay when desired. The gap may include material having a refractiveindex matched closely to glass or the layers on either side to reduceinternal reflection and/or depolarization effects. For the front displayor display layer 1, its backplane may be oriented opposite to that ofdisplay or display layer 2. In particular, for the front display 1 itsbackplane may be oriented to face the viewer to reduce internalreflections. Thus, it can be seen in FIG. 6 that the color filter layers(each of which may be made up of one or more layers) of the respectivedisplays 1 and 2 may be designed to face each other, with no liquidcrystal layer from either display being located between the color filterlayers of the first and second displays in certain example embodiments.In certain example embodiments, to reduce external reflections ofambient light, there may be provided an antireflective system at thefront such as that shown in FIG. 6 made up of quarter wave retarder andan antireflective polarizer, so that ambient light that would normallybe reflected would undergo a quarter wave rotation on the first passthrough the AR polarizer, is reflected by the backplane elements,undergoes a second rotation through the quarter wavelength retarder. Bythe time it goes through this second rotation, it is substantiallyorthogonal to the transmission axis of the AR polarizer and thus will besubstantially absorbed. Additionally, black mask (BM) or othernon-reflective material may be added behind the conductive traces of thedisplays to reduce reflections. Additionally, antireflective (AR)coating(s) may be applied to the interior surfaces in certain exampleembodiments of this invention. The AR coating may, for example, operatein the visible range, e.g., moth eye, single layer interference,multi-layer interference, etc.

Regarding a refractive beam mapper (RBM), such a beam mapping element ismade up of, or includes, a plurality of micro□lenses and may be used asa stand-alone element for reducing moire interference via pseudo randommapping (e.g., see FIGS. 4-6 and 14-16). In certain example pseudorandom mapping embodiments (e.g., FIGS. 4-5), each of the refractivemicro□lenses of an RBM may be designed to direct incident rays from theback LCD 2 to an observer in a defined path, each ray passing through adifferent sub□pixel in the front LCD 1 according to a pseudo randommapping. For example, FIG. 4 shows the pseudo random mapping of rearsubpixels or pixels of rear display 2 to subpixels or pixels in thefront display 1 (the rear display is the left-most display in FIG. 4).The pseudo random mapping is used in order to not introduce extra moireeffects, and can reduce moire interference. In an example embodiment,the divergence of these individual beams is limited so that light fromany pixel or subpixel of the rear LCD is not diverted more than onepixel or subpixel distance from a straight line on the front display.Optionally, the RBM may be laminated to the top LCD 1 (see FIGS. 5, 14and 16), and optionally matched or substantially matched optically tomedia between the two LCDs with a non□birefringent material. However, inother embodiments, the refractive beam mapper can be placed anywherewithin the LCD stack. FIG. 5 for instance shows the beam mapping element(e.g., RBM including a micro-lens array) located between the front andrear LCDs and laminated to an interior side of the front display.

In certain example embodiments, the micro-lenses of an RBM may befabricated using gray-scale lithography, to produce arbitrary surfacestructures in a micro-lens format. Each lens element may configured fordirecting light in a controlled direction enabling arbitrary andasymmetric scattering angles as shown in FIGS. 4-5. It is possible tomake a master to replicate the RBM using a variety of high-volumemanufacturing processes and materials as in the replication ofmicro-lens features, profile slope angle is more important than profileheight. FIGS. 4-5 show how the refractive beam mapper superimposes raysfrom the back LCD 2 onto the front LCD 1 from an observer's point ofview. The beam paths are mapped in a pseudo random fashion so not tointroduce other artifacts such as extra moire. The underlying LCDstructure 2 is randomized and thus incapable of generating significantmoire interference with the top LCD 1.

Alternatively, a diffuser may instead be used for the construction of amoire suppression element. While the process can be adapted to make arefractive beam mapper, engineered diffusers can also be used as optimaldiffuser elements for more reduction. Diffusers are not as desirable asa refractive beam element.

The refractive beam mapper may exhibit various features. For example, anRBM may exhibit achromatic performance. In addition, an RBM may exhibitarbitrary/asymmetric scattering angles. Further, an RBM may exhibitcontrolled intensity distribution patterns (e.g., circular, square,rectangular, elliptical, line, ring, etc.). Also, an RBM may exhibitcontrolled intensity profiles (e.g., flat top, Gaussian, batwing,custom, etc.). An RBM may also exhibit high optical transmissionefficiency (e.g., 90 percent). Additionally, an RBM may exhibit thepreservation of polarization. An RBM may be of or include variousmaterials, such as polymer injection molding, hot embossed polymers,polymer-on-glass components, etc.

Moiré interference in MLD is commonly suppressed by adding a diffuserelement (as opposed to a beam mapping element) between the back LCD andthe observer so that the pixel structure in the back LCD is blurred. Thegreater the diffuser spread the less the moire but correspondingly theobserved resolution of the back LCD is reduced. This becomes anoptimization problem and can be described as an image quality costfunction IQC which can range from 0 to 4, 0 being perfect and 4 beingworst for both moire and blurring. Factors to consider includecontrast=(max-min)/(max+min) where (1 is best, 0 is worst); crosstalk=1-contrast of alternating black and white lines (range 0:1);moiré=contrast of moiré for constant white pattern on both LCD's (range0:1); IQC=moiré_X +moiré_Y+crosstalk_X+crosstalk_Y (i.e. range is 0:4),the lower this value, the better. Normally the cost function would havea realistic maximum of approximately 2 as shown by the following limits:no diffuser:moiré_X +moiré_Y=2, crosstalk_X+crosstalk Y=0; and strongdiffuser:moiré_X+moiré_Y=0, crosstalk_X+crosstalk_Y=2.

FIG. 7 illustrates a bandwidth limited implementation of an RBM havingcustom refractive optics which are close to a flat top profile, suchthat the far field pattern is as close as possible to a flat topprofile. The prescription for the set of lenses that comprise thedistribution is defined, including feature sizes and slope angles basedon the scatter requirements. These parameters may be defined in terms ofprobability distribution functions that specify the likelihood that acertain lens will assume a specific prescription. A spatial distributionof the microlenses to create the surface structure is designed to createthe surface structure according to a desired distribution function. Itis appreciated that any underlying periodicity in the spatialdistribution of the microlenses may be eliminated in certain exampleembodiments. Also, lens mismatches may be eliminated, wherein lensmismatches can lead to wide-angle scatter, are eliminated. Both of theseimprovements maximize the use of available light. FIG. 8 shows anintensity profile exhibiting a much improved super-Lorentzian behaviorover the entire range of angles with p=40, and lens feature sizes≦160μm. The careful pseudo randomization of the surface structure alsocreates a scatter distribution that is devoid of artifacts and inducedmoire. This may be significant as regular patterns can introduceadditional moire interference.

FIG. 9 shows that there is a tradeoff between microlens size andintroduced image artifacts. Bigger microlenses will typically havebetter anti-moiré diffuser profiles. If the microlenses become of a sizethat are visible to the naked eye, then extra image artifacts willbecome apparent. These include sparkle, pixel walking and moreinterference between the pattern and either or both LCDs. FIG. 9illustrates PSF for a single microlens for various values of diameters(um). Minimizing feature size may also be utilized in the design of anLCD moire reduction element. The feature size should ideally be smallerthan a sub pixel in order to remain substantially invisible to the nakedeye as shown in FIG. 4. In the case where scatter centers take the formof microlenses, the feature size is given by the microlens diameter. Inparticular, miniature refractive elements are desired. If themicrolenses become of a size that are visible to the naked eye thenextra image artifacts will become apparent. These include sparkle, pixelwalking, and moire interference between the pattern and either or bothLCDs. Sparkle is most often seen in anti-glare displays where thedisplay surface has been treated to produce a matte textured surface.These surface features act as refractive or diffractive elements and caneither focus or defocus individual pixel elements depending on theviewer position leading to intensity variations or sparkle. Pixelwalking is the result of the refractive distortion appearing to move anddistort the individual pixels and the viewer moves position. Extra moireinterference is introduced when regular features in the array ofmicrolens “beat” with one or both of the LCDs. Randomization andreduction of lens size in an RBM or diffuser and placement reduce theseextra moire artifacts. There are two factors to consider in this regard,sag and averaging. To ensure the best uniformity and reduction in moiré,a large number of scatter centers should be illuminated within eachpixel area as shown in FIG. 4. At the same time, for a certain set ofparameters (e.g., spread angle, index of refraction, and conicconstant), the lens depth decreases as the microlens diameter decreases.If the process continues, a diffractive regime is eventually reachedwhere the lens depth only imparts a phase delay that is a small fractionof 2π. In this respect, it is useful to define the phase number in thefollowing equation:

$M = {\frac{y_{\max}}{( \frac{\lambda}{\Delta \; n} )}.}$

In the above equation, ymax represents the total lens sag, λ is thewavelength under consideration, and Δn equals n(λ)1, with n the index ofrefraction at wavelength λ, for an element in air. The phase numberbasically expresses the total sag in the language of phase cycles anddefines the regime, diffractive or refractive, the microlens operateson: M=1 implies a diffractive element with exactly 2π phase shift. Inone embodiment, for a microlens to operate in the refractive regime, asis desirable for an achromatic component with high target efficiency,the phase number M should be as large as possible.

Consider again the case of a microlens that scatters a collimated beamwith a 40° spread. As the diameter gets smaller the farfield scattershows coarser oscillations and more sloped falloff, translating intolower target efficiency. A simple rule of thumb to help decide theminimum feature size or lens diameter to utilize is given by thefollowing equation.

$D \geq {230M{\frac{\lambda}{\theta_{0}}.}}$

In the above equation, θ₀ is the halfwidth beam spread angle in degrees(in air). To be well within the refractive regime, M should be around 8or more. Assuming θ=2° and λ=0.633 μm, and M=8, a result for D≧582 μm isobtained, which is too large compared with a 200 um pixel and will bevery visible, degrading the image. Increasing the spread to 20 degreewill reduce D by a factor of 10 to 58 μm. In the above equation, thecloser the diffuser is to the back panel, the greater the FWHM angle θ₀.The equation also gives a rule of thumb of microlens diameter to θ₀.

Embedding the refractor in a medium of higher refractive index (RI) suchas silicon OCA, rather than air, allows for the effective use of a widerangle refractor, as the higher RI will reduce the refractive power ofeach microlens. With an RI=1.42, θ₀ equates to an angle of θ=˜11° or bythe above referenced equation, D≧105 μm which is more acceptable. In oneembodiment, embedding in high RI material effectively reduces themicrolens diameter, which results in less image artifacts. Specifically,replacing the air between the two panels with an indexed matched mediumwill also allow smaller divergence angles as measured in air and thussmaller microlens diameters.

FIG. 10 shows the fabrication process of an RBM, in accordance with oneembodiment of the present disclosure in the above respects, includingthe formation of microlenses on a wafer support. The RBM may be embeddedin high RI material to reduce Fresnel depolarization, in order toimprove image contrast of the MLD.

FIG. 11 shows a microlens surface, which typically has a distribution ofsurface normals between 0 and approximately 20 degrees. The distributionof surface normals leads to contrast reduction because S and Ppolarizations are transmitted with different attenuations. FIG. 12 showscurves illustrating the transmission coefficient for S and P waves vs.angle of incidence, and FIG. 13 shows system contrast (contrast (θi, n1,n2, N), wherein θi is the angle of incidence, n1 is the refractive indexof the material between LCDs, n2 is the refractive index of glass, and Nis the number of interfaces. As shown the line to the far right with theRI at 1.4 and 1.5 shows the best contrast as the Fresnel depolarizationis the least.

FIGS. 14-16 show various placements of the moire reduction element(e.g., refractive element such as RBM). In FIGS. 14 and 16 for example,the moire reduction element could be positioned on the top surface ofthe front display 1 as a laminatable film with the patterned surfacefacing downwards to get the feature size small, as previously described.These embodiments may or may not be used in combination with subpixelcompression techniques. In one embodiment, having the patterned surfacefacing upwards would also act as an anti-glaring mechanism, but it willbe necessary to embed in optical coupling adhesive (OCA) with arefractive index of approximately 1.5 to achieve a feature size smallerthan 70 μm. Alternatively, as shown in FIG. 15, it is also possible toplace the moire reduction element between two LCDs (e.g., laminated tothe rear display) where the divergence will be larger, and thus thefeature size smaller. Index matching the internal voids with a materialof R.I. greater than 1.4 (see OCA) will greatly reduce Fresneldepolarization, thereby improving contrast and reducing reflections. Theinternal voids index matched with glass and OCA to reduce Fresnelpolarization also improve contrast and reduce reflections. In oneembodiment, the FWHM width for this implementation may be about 1.8degrees, with a square profile.

It has surprisingly been found that use of a square diffuser profile(e.g., as viewed from above), as shown in FIG. 17, has advantageoustechnical qualities in connection with refractive beam mappers describedherein, according to any embodiment of the instant disclosure. In otherwords, a square profile diffuser such as shown in FIG. 17 may be usedfor any of the refractive beam mappers in this disclosure, in certainexample embodiments of this invention. A beam mapping element includingan array of square microlenses such as that shown in FIG. 17 may bemade, for example, by projecting a shaped laser beam into a photoresist,so that each microlens is a copy of the prior, in certain exampleinstances. The beam mapping element of FIG. 17 may be used in anyembodiment herein, such as for the refractive beam mapper in any ofFIGS. 4-7, 14-16.

FIG. 18 is, for purposes of comparison, representative of a perfectcircular filter kernel—that is there is no energy outside the boundaryof the circle. This kernel is convolved with an image of a pixel todetermine the point spread of the system impulse response—a single blackpixel. In FIG. 19, the radius of the circle is varied and applied to theimage to determine the optimum. The blue line below is representative oftotal image quality and incorporates the blur and residual pixel moire.Note the minimum of the function is optimum. As can be seen in the pixelimage to the top right in FIG. 19, a circular kernel never completelyquells the sub-pixel structure. This in turn would give rise to someresidual moire in the MLD system.

In contrast, a square or substantially square shape (e.g., see FIG. 17)will completely or substantially remove any residual moire in a MLDsystem. FIG. 20 shows a comparison between the square average filter(e.g., line trending higher to the right) and the round disk filter.Note that model pixels are 150 microns high/wide, and so the optimumsquare filter kernel has the same size and width as the pixel as viewedfrom above. It can be seen in FIG. 20 that the square shaped diffuserprofile has improved image quality cost function compared to thecircular shape. The far field profile of the diffuser affects costfunction. A square engineered diffuser is almost twice as good as around diffuser. In FIG. 20, IQC is shown for round and square profilesusing 150 μm diameter (length and width) pixels. The cost is minimizedfor the square case when the entire pixel is covered (i.e., the squareradius=75 μm or width=150 μm).

In square lens profile embodiments, the microlenses are characterized bya phase number M of 8 or more, more preferably of 16 or more, and it hasbeen found that this improves image quality.

While the foregoing disclosure sets forth various embodiments usingspecific block diagrams, flowcharts, and examples, each block diagramcomponent, flowchart step, operation, and/or component described and/orillustrated herein may be implemented, individually and/or collectively,using a wide range of hardware, software, or firmware (or anycombination thereof) configurations. In addition, any disclosure ofcomponents contained within other components should be considered asexamples because many other architectures can be implemented to achievethe same functionality.

The process parameters and sequence of steps described and/orillustrated herein are given by way of example only and can be varied asdesired. For example, while the steps illustrated and/or describedherein may be shown or discussed in a particular order, these steps donot necessarily need to be performed in the order illustrated ordiscussed. The various example methods described and/or illustratedherein may also omit one or more of the steps described or illustratedherein or include additional steps in addition to those disclosed.

While various embodiments have been described and/or illustrated hereinin the context of fully functional computing systems, one or more ofthese example embodiments may be distributed as a program product in avariety of forms, regardless of the particular type of computer-readablemedia used to actually carry out the distribution. The embodimentsdisclosed herein may also be implemented using software modules thatperform certain tasks. These software modules may include script, batch,or other executable files that may be stored on a computer-readablestorage medium or in a computing system. These software modules mayconfigure a computing system to perform one or more of the exampleembodiments disclosed herein. Various functions described herein may beprovided through a remote desktop environment or any other cloud-basedcomputing environment.

The foregoing description, for purpose of explanation, has beendescribed with reference to specific embodiments. However, theillustrative discussions above are not intended to be exhaustive or tolimit the invention to the precise forms disclosed. Many modificationsand variations are possible in view of the above teachings. Theembodiments were chosen and described in order to best explain theprinciples of the invention and its practical applications, to therebyenable others skilled in the art to best utilize the invention andvarious embodiments with various modifications as may be suited to theparticular use contemplated.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the present invention, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed, that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present invention. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or steps.

In example embodiments of this invention, there is provided a displaydevice comprising: a first display in a first plane for displaying afirst image; a second display in a second plane for displaying a secondimage, wherein said first and second planes are approximately parallelto each other; a beam mapping element located between the first andsecond displays and comprising a plurality of microlenses configured todirect rays output from the second display through sub-pixels of thefirst display and toward a viewer, wherein the microlenses each have asubstantially square profile as viewed from above in order to improveimage quality.

In the display device of the immediately preceding paragraph, the beammapping element may comprise a refractive beam mapper.

In the display device of any of the preceding two paragraphs, the beammapping element may be configured to direct rays output from the seconddisplay in a pseudo random manner through sub-pixels of the firstdisplay and toward a viewer.

In the display device of any of the preceding three paragraphs, the beammapping element may have asymmetric scattering angles.

In the display device of any of the preceding four paragraphs, the beammapping element may substantially preserve polarization.

In the display device of any of the preceding five paragraphs, the beammapping element may have refractive optics for realizing substantially aflat top profile, such that a far field pattern of output is close to aflat top profile.

In the display device of any of the preceding six paragraphs, the beammapping element may limit divergence from any point on the seconddisplay to less than a distance of one pixel offset when the raysproceed through the first display.

In the display device of any of the preceding seven paragraphs, each ofthe microlenses may have a diameter no greater than a length and/or awidth of a subpixel in the second display.

In the display device of any of the preceding eight paragraphs, themicrolenses may be characterized by a phase number M of 8 or more.

In the display device of any of the preceding nine paragraphs, themicrolenses may have a distribution of surface normals between 0 andapproximately 20 degrees.

In the display device of any of the preceding ten paragraphs, the beammapping element may be laminated to the second display.

In the display device of any of the preceding eleven paragraphs, curvedsurfaces of the microlenses face a viewer and/or contact a refractiveindex material having a refractive index of at least 1.4.

In the display device of any of the preceding twelve paragraphs, thesecond display may be a rear display, and the first display may be afront display, of the display device.

In the display device of any of the preceding thirteen paragraphs, raysfrom a given subpixel in the second display may be directed towardmultiple different subpixels of the first display, and rays from aplurality of different subpixels of the second display may proceedthrough a given subpixel of the first display.

Embodiments according to the present disclosure are thus described.While the present disclosure has been described in particularembodiments, it should be appreciated that the disclosure should not beconstrued as limited by such embodiments.

1. A display device comprising: a first display in a first plane fordisplaying a first image; a second display in a second plane fordisplaying a second image, wherein said first and second planes areapproximately parallel to each other; a beam mapping element locatedbetween the first and second displays and comprising a plurality ofmicrolenses configured to direct rays output from the second displaythrough sub-pixels of the first display and toward a viewer, wherein themicrolenses each have a substantially square profile as viewed fromabove in order to improve image quality.
 2. The display device of claim1, wherein the beam mapping element comprises a refractive beam mapper.3. The display device of claim 1, wherein the beam mapping element isconfigured to direct rays output from the second display in a pseudorandom manner through sub-pixels of the first display and toward aviewer.
 4. The display device of claim 1, wherein the beam mappingelement has asymmetric scattering angles.
 5. The display device of claim1, wherein the beam mapping element substantially preservespolarization.
 6. The display device of claim 1, wherein the beam mappingelement has refractive optics for realizing substantially a flat topprofile, such that a far field pattern of output is close to a flat topprofile.
 7. The display device of claim 1, wherein the beam mappingelement limits divergence from any point on the second display to lessthan a distance of one pixel offset when the rays proceed through thefirst display.
 8. The display device of claim 1, wherein each of themicrolenses has a diameter no greater than a length and/or a width of asubpixel in the second display.
 9. The display device of claim 1,wherein the microlenses are characterized by a phase number M of 8 ormore.
 10. The display device of claim 1, wherein the microlenses have adistribution of surface normals between 0 and approximately 20 degrees.11. The display device of claim 1, wherein the beam mapping element islaminated to the second display.
 12. The display device of claim 1,wherein curved surfaces of the microlenses contact a refractive indexmaterial having a refractive index of at least 1.4.
 13. The displaydevice of claim 1, wherein the second display is a rear display, and thefirst display is a front display, of the display device.
 14. The displaydevice of claim 1, wherein rays from a given subpixel in the seconddisplay are directed toward multiple different subpixels of the firstdisplay, and wherein rays from a plurality of different subpixels of thesecond display proceed through a given subpixel of the first display.15. A method of displaying an image via a display device including afirst display in a first plane for displaying a first image, and asecond display in a second plane for displaying a second image, whereinsaid first and second planes are approximately parallel to each other,the method comprising; directing light rays output from the seconddisplay through sub-pixels of the first display and toward a viewer, viaa plurality of microlenses having a substantially square profile asviewed from the point of view of a viewer, the microlenses being locatedbetween the first and second displays.
 16. The method of claim 15,wherein the microlenses are laminated to the second display.
 17. Themethod of claim 15, wherein the second display is a rear display, andthe first display is a front display, of the display device.
 18. Themethod of claim 15, wherein rays from a given subpixel in the seconddisplay are directed toward multiple different subpixels of the firstdisplay, and wherein rays from a plurality of different subpixels of thesecond display proceed through a given subpixel of the first display.19. A display device comprising: a first display in a first plane fordisplaying a first image; a second display in a second plane fordisplaying a second image, wherein said first and second planes areapproximately parallel to each other; a refractive beam mapper locatedbetween the first and second displays and comprising an array of beammapping elements configured to direct rays output from the seconddisplay through sub-pixels of the first display and toward a viewer,wherein the beam mapping elements each have a substantially squareprofile.